Acute allergic conjunctivitis is an inflammation of the conjunctiva, typically resulting from hypersensitivity reactions to various types of allergens. These hypersensitivity reactions involve allergen induced, immunoglobulin E (IgE)-mediated release of histamine and other mediators from mast cells and basophils. Mast cell degranulation leads to release of inflammatory mediators, such as cytokines and prostaglandins, and activation of enzymatic cascades generating pro-inflammatory mediators. In the eye, these biological events lead to inflammation of the conjunctival mucosa that also affects the cornea and eyelids, with symptoms that include itching and burning, tearing, chemosis (conjunctival edema), conjunctival injection, hyperemia, eyelid edema, and mucus discharge.
Allergic conjunctivitis disorders can be grouped into seasonal allergic conjunctivitis (SAC) and perennial allergic conjunctivitis (PAC). In SAC, recurrent allergic conjunctivitis is caused by environmental exposure to seasonal allergens, such as ragweed and pollen, whereas with PAC, afflicted subjects have year-round symptoms that are most commonly triggered by indoor allergens, such as mold, animal dander, dust mites, and feathers. Both acute conditions usually have bilateral involvement, but the symptoms of SAC are generally more severe than those related to PAC.
Various treatments have been developed for treating allergic conjunctivitis, including topical antihistamines, nonsteroidal anti-inflammatory drugs, corticosteroids, and immune response modulators. For example, an exemplary course of treatment have used antihistamines, such as pheniramine, antazoline, levocabastine and emadastine, but these compounds have limited anti-inflammatory effects and duration of efficacy. Current therapies for the management of allergic conjunctivitis are drugs having both anti-histaminic and mast cell stabilizing properties such as olopatadine, ketotifen and azelastine. However, these compounds often fail to provide relief of more than one ocular allergy symptom and some of the known treatments with pharmaceutically active compounds can result in undesirable side effects, such as pain, swelling and vision changes.